The purpose of this project is to continue development and applications of a computer controlled, low-light microscopic system. This system consists of a digitally controlled SIT vidicon with a custom dual MCP intensifier, microscopic optics, illumination optics, custom mechanical components and the computer system. The instrument has been used to detect faint light from self-luminous microscopic sources. It has both fluorescence and bioluminescence capabilities. The software complement includes programs for image enhancement, frame averaging, file storage, kinetic studies, and display and plotting of computerized images. Using this instrument we have successfully monitored transient release of calcium inside of cells during stimulus response. For this work the calcium activated photoprotein, aequorin, which is collected and purified by personnel of this group, is used to monitor free calcium levels. The instrument system also allows detection of fluorescent loci within cells with the advantage that, due to its extreme sensitivity, much lower levels of exciting light are required thereby decreasing the effects of bleaching and photodegradation due to the exciting source. Continuation of this project will involve measurements of intracellular calcium levels in a variety of animal and plant cells. Studies of localization of various labeled proteins will also be carried out.